1. Repeatability of Anterior and Posterior Corneal Higher- Order Aberrations in 4 mm, 6 mm and 8 mm diameters measured by Pentacam System
Jadwiga Wojtowicz MD, Orkun Muftuoglu MD, Engy Mohamed MD, V. Vinod Mootha MD, R.Wayne Bowman MD, H. Dwight Cavanagh MD, James P. McCulley MD, FRCOphth. UT Southwestern Medical Center. Department of Ophthalmology. Aston Ophthalmology Clinic, Dallas, TX.
Financial Disclosure for all authors: *JPM: Consultant for Alcon Inc. (Fort Worth, TX) *JW, OM, EM, VM, DC: none Acknowledgements: Supported in part by an unrestricted research grant from Research to Prevent Blindness, Inc., New York

2. INTRODUCTION
Eye aberrations plays a role in degrading retinal image quality.1
The distribution of the optical higher-order aberrations (HOAs) of the
anterior and posterior cornea are essential for understanding the
physiological optics of the eye and enhanced the outcomes of
wavefront-guided therapies.
It is well known that pupil diameter aperture changes influence HOAs. 2
Evaluating the intra-subject variability of anterior and posterior corneal HOAs at different pupil diameter areas with Pentacam will allow us:
To evaluate corneal HOAs distribution in normal subjects.
The variability of repeated scans measured with the Pentacam system.
Liang J, Williams DR. Aberrations and retinal image quality of the normal human eye. J Opt Soc Am A 1997;14:
Buhren J, Kuhne C, Kohnen T. Influence of pupil and optical zone diameter on higher-order aberrations after wavefront-guidede myopic LASIK. J Catract Refract Surg 2005;31:

3. METHODS Scheimpflug system (Pentacam Oculus, Inc.) was used to measure
HOAs.
Inclusion criteria: no symptoms or signs of ocular disease, other than
refractive error, detected by history, slit lamp examination and fundoscopy
Exclusion criteria:
Dry eye patients
Non-contact lens wearers
Retinal disease
Any systemic disease, the use of any eye-drops or oral medication
that might affect the ocular surface.
Six consecutive measurements were performed in each subject in
both eyes in one visit by the same operator.
The parameters analyzed were Zernike coefficients from 3rd to 8th
orders from anterior and posterior cornea within a 4mm, 6mm and
8 mm diameter pupil area.

4. METHODS Statistical Analysis
SigmaStat 2.03 Software (Systat Software Inc, Richmond, California,
USA) was used.
To study the intra-subject reproducibility of ocular HOA, SD and
coefficient of variation (CV= SD/mean) were calculated.

5. Coefficient of variation (CV) of Corneal HOA
RESULTS
The study group consisted of 50 eyes from 25 normal subjects
(13 females and 7 males). The mean age was years
Coefficient of variation (CV) of Corneal HOA
Anterior
Posterior
Corneal HOA
8 mm
6 mm
4 mm
8mm
6mm
4mm
Spherical
2.1
8.5
13.6 7
6.5
12.1
Coma
7.3
12.4
31.7
9.3
16.3 35
Trefoil 21 23 32 22 28
CV expressed as %
Among the different zernike terms generated by Pentacam, Spherical aberrations was the most repeatable

6. Mean and SD for absolute Zernike coefficients from anterior and posterior corneal HOAs for 8, 6 and 4 mm diameter pupil area.
Anterior
Posterior
Zernike
Mode
8 mm
6 mm
4 mm
8mm
6mm
4mm
Z3-1
0.541± 0.150
0.304± 0.094
0.143± 0.062
1.057± 0.579
0.622± 0.280
0.399±0.216
Z 3-3
0.137± 0.085
0.134±0.83
0.162± 0.078
0.487± 0.277
0.353±0.196
0.350± 0.173
Z4-0
1.381±0.160
0.551±0.102
0.162± 0.042
2.640± 0.633
1.404±0.303
0.503± 0.114
Z4-2
0.166 ± 0.077
0.109±0.059
0.056± 0.029
0.562± 0.258
0.356±0.172
0.172± 0.081
Z4-4
0.140 ± 0.101
0.139±0.071
0.087± 0.037
0.722± 0.315
0.594±0.225
0.313± 0.138
Z 5-1
0.052 ± 0.029
0.039±0.018
0.013± 0.006
0.527± 0.215
0.185±0.119
0.040±0.022
Z5-3
0.130 ± 0.061
0.076±0.036
0.022± 0.010
0.243±0.111
0.155±0.078
0.042± 0.024
Z5-5
0.113 ±0.037
0.052±0.030
0.015± 0.009
0.340 ±0.214
0.210±0.146
Z6-0
0.034 ± 0.022
0.015±0.009
0.002± 0.001
0.022± 0.104
0.099±0.052
0.014± 0.008
Z6-2
0.060± 0.030
0.023±0.011
0.004± 0.002
0.175± 0.082
0.089±0.039
0.017± 0.011
Z6-4
0.102± 0.037
0.044±0.019
0.008± 0.003
0.281±0.134
0.130±0.071
0.029± 0.027
Z6-6
0.089± 0.063
0.035±0.016
0.006± 0.003
0.385±0.243
0.163±0.104
0.026± 0.011

7. Pentacam image for anterior corneal HOAS

8. Pentacam image for posterior HOAS

9. CONCLUSIONS
Corneal higher-order aberrations between third and sixth order derived by Pentacam showed more repeatability for both anterior and posterior cornea.
Spherical HOAs showed higher repeatability than coma and trefoil. However Shankar et al 1, reported poor repeatability for HOAs measured with Pentacam, who exported the topographical maps to an external software for the analysis.
More variability for Zernike polynomials was found within smaller
measured zone.
The Zernike distribution in normal subjects for the posterior cornea showed greater values than the anterior cornea, with the exception of Z4-0
1. Shankar H, taranath D, Santhirathelagan ChT, Pesudovs K. Repeatability of corneal first-surface wavefront aberrations measured with Pentacam corneal topography. J. cataract Refract Surg. 2008;34: